Schwartz was a four-year letterman at linebacker for the Hoyas of Georgetown University, where he earned his degree in economics. He received Distinguished Economics Graduate honors at Georgetown and earned numerous honors in 1988, including Division III CoSIDA/GTE Academic All-America, All-America, and team captain.

The Lions started the 2012 season with a 4–4 record, but they then dropped their final eight games to end the year at 4–12.[13] They finished in last place in the NFC North, as every other division member won at least ten games.[14]

Following the season, Schwartz and his staff led the South Team to a 21–16 triumph in the 2013 Senior Bowl.[15]

The Lions started the 2013 season with a 6–3 record and gained control of the NFC North, the Lions proceeded to drop six of their next seven games to end the year at 7–9. Schwartz was fired on December 30, 2013, following five seasons as head coach.[16]

On January 24, Schwartz was hired by the Buffalo Bills as the defensive coordinator. In 2014 Schwartz's defense was one of the top defenses statistically in the NFL, and led the league in sacks.[17] During the 2014 season, the Bills went 4-0 against NFC North opponents, which Schwartz had coached against for the previous five seasons. On October 5, 2014, the Bills defeated Schwartz's former team, the Detroit Lions, by a final score of 17-14, in Detroit.[18] Schwartz was carried off the field after by his players after the game. Some Lions players, especially Golden Tate[19] were upset by Schwartz's decision to be carried off the field against his former team.

The Bills ended the season fourth in the NFL in points and yards allowed per game with 18.1 and 312.2, respectively, while ranking third in takeaways with 30.[20] The Bills also finished with their first winning record in ten years at 9-7. Despite the success, head coach Doug Marrone resigned at the end of the season, and new Bills coach Rex Ryan decided to bring in his own personnel, rather than retaining Schwartz.[21]